Doctor of Philosophy (PhD)
Plant Pathology and Crop Physiology
Cercospora leaf blight (CLB) caused in soybean by Cercospora cf. flagellaris is an important disease in Louisiana. It was thought that CLB starts with leaf purpling, and then, as the disease progresses, leaves become blighted. Moreover, it was assumed that accumulation of cercosporin, a red/purple pigment, was the cause of the purple pigmentation in diseased leaves. However, our observations in Louisiana suggested that these two symptoms were not correlated. The first objective of this work was to examine the relationship between purple and blight symptoms as well as their relationships with endophytic colonization of leaves by the fungus and accumulation of cercosporin in soybean leaves. The second objective was to document biochemical changes in purple, blighted and asymptomatic leaves. We demonstrated that purple and blighted leaves were not necessarily correlated, and that cercosporin concentrations in purple leaves were one third that in blighted leaves. Location and cultivar also determined the type of symptoms shown by soybean leaves. This work provides the first report of accumulation of coumestrol (COU) in purple leaves of soybean affected by CLB and demonstrated that COU may be associated with resistance to C. cf. flagellaris via its antioxidant activity. Production of pterocarpin derivatives, a common reaction to biotic and abiotic stresses, may be the cause of purple discoloration of soybean leaves affected by CLB. Results from this work showed that purple CLB leaf symptoms probably are a plant response to low levels of cercosporin produced by the pathogen in its endophytic stage, and blight symptoms are produced when cercosporin production by the pathogen exceeds the plant’s antioxidant capability.
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Chagas Ferreira da Silva, Eduardo, "Cercospora Leaf Blight of Soybeans:
Symptomatology and Biochemical Responses" (2017). LSU Doctoral Dissertations. 4317.